The present invention concerns an enzymatic oxidative deamination process to prepare an intermediate useful to prepare compounds having endopeptidase and angiotensin converting enzyme inhibition activity.
Robl in U.S. Pat. No. 5,508,272 discloses compounds of the formula 
wherein A is 
as possessing neutral endopeptidase and angiotensin converting enzyme inhibition activity. Among these compounds is [4S-[4xcex1(R*),7xcex1,10axcex2]]-octahydro-4-[(2-mercapto-1-oxo-3-phenylpropyl)amino]-5-oxo-7H-pyrido[2,1-b][1,3]thiazepine-7-carboxylic acid which is currently undergoing clinical evaluation. This compound is reported herein as (1).
Robl discloses that the amino lactam portion of (1), i.e., the intermediate 
can be prepared by coupling (S)-2-amino-6,6-dimethoxyhexanoic acid methyl ester with the N-protected amino acid 
wherein P1 is an amino protecting group and P2 is a sulfur protecting group to give the dipeptide of the formula 
Removal of the P2 protecting group, followed by acid catalyzed cyclization, and removal of the P1 protecting group gives [4S-(4xcex1,7xcex1,10axcex2)]-octahydro-4-amino-5-oxo-7H-pyrido[2,1-b][1,3]thiazephine-7-carboxdylic acid, methyl ester.
Robl discloses preparing (S)-2-amino-6,6-dialkoxyhexanoic acid, alkyl ester, such as (S)-2-amino-6,6-dimethoxyhexanoic acid, methyl ester, by converting N-protected L-xcex5-hydroxynorleucine to its methyl ester, oxidizing to a corresponding aldehyde, such as of the formula 
then reacting with trimethyl orthoformate in the presence of a strong acid catalyst, and removing the P3 protecting group.
The present invention provides an enzymatic process for the preparation of the above-described intermediate, i.e., the protected amino lactam portion of (1).
More specifically, the present invention is directed to a process for preparing an amino lactam compound of the formula I 
comprising contacting a dipeptide monomer of the formula II 
wherein P1 is an amino protecting group, and R1 is H, alkyl or of the formula 
wherein R2 is alkyl,
with an aminotransferase enzyme in the presence of xcex1-ketoglutarate under conditions suitable for formation of the compound of formula I. The immediately preceding process will be referred to herein as the xe2x80x9coxidative deaminationxe2x80x9d process.
In an alternate embodiment, the oxidative deamination process is performed in the presence of a glutamate oxidase enzyme which functions to recycle glutamate formed during the process back to alpha-ketoglutarate.
The present invention is also directed to a process for preparing a dipeptide monomer starting compound of the formula III 
comprising contacting a dipeptide dimer compound of the formula IV 
wherein P1 is as defined above,
with a reducing agent under conditions suitable for formation of the compound of formula III. The immediately preceding process for preparing the dipeptide monomer will be referred to herein as the xe2x80x9creductionxe2x80x9d process.
The present invention also concerns an engineered host cell containing recombinant nucleic acid capable of expressing an aminotransferase enzyme. In addition, the invention concerns a novel aminotransferase from Spingomonas sp. and nucleic acid encoding same.
The present invention also concerns the novel compounds of formulas II, III and IV.